Method and apparatus for coating



C. A. DAVIS METHOD AND APPARATUS FOR COATING Filed Feb l III f/ Il!.fllllllll In Oct. 22, 1929.

.GMA 0,

INA/ENTOR 6L V l 'Ii l A ,M

atentecl Oct. `22, 1929 PATENT OFFICE CHARLES A. DAVIS, F YOUNGS'IOWN,OHIO METHOD AND APPARATUS FOR COATING Application filed February lhepresent invention relates broadly to the art of coating, and method ofproducing the same, and more particularly to this art as applicable tothe production of galvanized articles or bodies.

This invention may .be utilized, not only in connection with sheets,bars, special shapes and the like, but in 'connection with any articleson which the particular coating produced by my invention is desired.Throughout the specification and claims therefore I use the termarticles in its generic sense as definitive of the wide variety ofshapes and articles to which galvanizing may be i5 applicable.

At the present time it is customary to galvanize by employing a bath ofzinc and tin; zinc, lead and tin; zinc, lead, tin and aluminum or zinc,tin and aluminum, or any other zo desired combination of metals capableof producing the type of coating desired. My invention may be used withcoating baths having any of these different characteristics, and it willtherefore be understood that the term coating is used in its genericsense as definitive of a protective layer or body without regardspecifically to the combination` thereof.

H eretofore, in the art to which the present invention relates, when ithas been desired to produce dull finished coated articles, such assheets, it has been customary to pass the same through a bath having itstemperature increased from the usual point of SOOO to 8500 F. to ahigher range of from 1000c to 1050O F.

This, however, has involved. many difficulties, and has not resulted 1n`a referred to tends to cause the formation of f vquently, s0 calledfreak sheets have been Y 12, 1925. Serial N0. 8,683.

produced havinor a noneuniform coating. This has been dane partly to thedross re-4 ferred to, but largely to the wiping-action of the rollswhich have been loaded or otherwise held together to tightly engage thesheet or other article. The result has been a varying pressure atdifferent parts of the sheet,` this usually being greatest in the centerand least at the edges, resulting in a sheet having a central portion ofdark color approximating that of the base metal, and edge portions witha gradually thickening coat.

As the coated article has left the bath, usually by passage between apair of exit rolls where it has been a sheet, or by suitable conveyorsor the like where it has other characteristics, it has been subjected tothe cooling action of the atmosphere, or to a blast of cooling air. Ihave found that the result of such cooling is to cause the sheet tospangle, this being due to crystallization or the formation of cr stalsbefore a proper bond has been effected7 between the coating and the basemetal.

I have found that the difficulties and 0bjections to the methods asheretofore practiced for the production of a dull galvanized finish maybe entirely overcome and obviated by the present invention. At the sametime, there may be produced an article having a heavier weight of tightcoating per unit of y area together with increased ductility withoutfear o f checking or peeling, and these constitute certain of' theobjects of the present invention.

In the accompanying drawings I have shown for purposes of illustrationonly certain preferred embodiments of the present invention,particularly as applicable to the art of galvanizing sheets, it beingunderstood however that the drawings do not define the limits of myinvention as changes in the construction of the apparatus and theoperation, as adaptable to the different shapes or articles beinghandled, may be made without departing either from the spirit of theinvention or Ascope of my broader claims.

In the drawings:

Figure l-is a longitudinal sectional view through a portion of one formof apparatus embodying the present invention; and

Figure 2 is a transverse sectional view, on an enlarged scale, on theline II-II of Figure l. l .f

In carrying out the present invention there may be utilized a suitableform of pot or galvanizing tank 2 of any desired construction suitablefor the type of bath and type of material being coated. In theillustrated embodiment of the invention', I have shown a pot especiallyadaptable to the coating of sheets, and for this reason it is shown asprovided with guides 3 adapted to deliver the sheets successively to apair of exit rolls 4 located adjacent the surface of the bath B withinthe pot.

Disposed above the exit rolls, and in cooperative relation thereto, insuch manner as to engage a sheet s as it is delivered by the exit rolls,is a guide or deflector 5 which may be in the form of a heat retaininghood if desired, and adapted to deflect the sheet laterally as indicatedin dotted lines in the drawings. Mounted in such manner as to receive adeflected sheet is a conveyor 6 of any desired construction preferablyguided by a roll or set of rolls 7 mounted on the pot and passing to asecond roll or set of rolls 8 mounted at any desired distance'therefrom. Conveniently, these rolls may be in the form of sprockets anyor all of which may be driven to effect the desired movement of theconveyor, or additional driving means may be provided as well understoodin the art.

Intermediate the ends of the conveyor there is provided means lforsubjecting the succes- A sive sheets to predetermined temperatureconditions or Zones whereby the rapidity of cooling may be accuratelyand definitely con'- trolled. Breferably, this operation is obtained byproviding a leer or leer tunnel 9 having suitable supporting means 10therein for the upper run of the conveyor. Conveniently, this supportingmeans may be in the form of a continuously extending sheet or partitioncarried bythe sides of the leer and 'adapted to effect a more nearlyuniform distribution of heat to the coated articles as will hereafter bemore fully pointed out. The upper portion of the leer may be providedwith an easily removable cover or closure 11 whereby access to theinterior thereof is facilitated.

Mounted at suitable points within the leer, and preferably below thepartition 10 is means for producing definite temperature conditionsthroughoutthe length of the leer. In accordance with the illustratedembodiment of the invention these temperature conditions may be obtainedby utilizing a plurality of transversely extending burners l2, suitablyspaced, and each provided with a controlling valve 13 whereby the amountof gas or other combustible material supplied thereto may be effectivelycontrolled. In actual operation, these burners will preferably be socontrolled as to provide a gradually decreasing temperature conditionfrom the entering end 14 of the leer to the exit end 15, whereby thetemperature of the sheet, or other article, will be gradually broughtfrom its high point to a lower temperature condition without, permittingcrystallization or Spangling to occur.

It will be understood that the heating medium utilized for the leer isimmaterial, as is also the type of heater employed, it being possible touse any type of heating means operative either from the standpoint ofdirect heat transfer, or reflective heat transfer, as desired.

In accordance with the present invention, the bath B is maintained atits normal point of approximately 800o to 850 F. At this temperature,the formation of dross is at a minimum, and it is not suspended in thebath in such manner as to interfere with the production of an effectivecoating. At this temperature also, the apparatus may be effectivelyoperated, as the conditions are not such as to so influence the sameasis the case where higher temperatures, approximately of 1000o F. orover, have heretofore been employed. I have found that where normaltemperature conditions are used, there is a tendency for the coating tocrystallize as the article leaves the bath due probably to the coolingaction either of the atmosphere or air blast before the article and thecoating have become firmly united. Obviously, this is abjectionable asit permits the coating later to peel or flake away from the articleparticularly as it is bent or flexed from its normal position. I havefound that this condition may be entirely overcome by subjecting thearticle to such temperature conditions substantially at the time itleaves the bath to prevent such crystallization. These temperatureconditions may obviously be obtained in many ways, but I have found thatthey may expeditiously be created by the use of a burner or burners 16located adjacent the exit rolls and effective for directing a blast orblasts against the articles after they have left the bath. By properlypositioning such burners, burning of the coating does not take place,and the temperature of the article is maintained at a point above thatat which crystallization is possible. If desired supplemental burners 17may be provided intermediate the burners 16 and the leer for the purposeof further controlling the temperature of the coated articles.

' A further difiiculty, heretofore encountered in the art has been duepartly to the action of the conveyors on the coated articles.Ordinarily, the `conveyors have been at a materiallyv lower temperaturethan the articles, and along the lines of contact between the articlesand the conveyors there has been such vtitl a chilling action as tomaterially augment this crystallization. This augmenting has resulted innon-uniformity of the product. By the apparatus disclosed herein, theconveyors are maintained at the desired temperature to obviate thischilling action, not only by the burners 16 and 17 but also, if desired,by returning the lower run of the conveyor through the leer.' In actualpractice, Where the conditions are such that a leer cannot beconstructed of such nature as to' permit both runs of the conveyor totravel therethrough, I have found that the burners provided, are, ifproperly controlled, effective for maintaining a temperature such `that'chilling does not take place.

I have found also that certain of the advantages of the presentinvention are inherent in the application of heat t0 a coated articleirrespective, to some extent, of the possible previous formation of acrystalline or semicrystalline structure, due to the fact that theincreased temperature to which the coating is subjected tends to improvethe bond between such coating and thereby impart increased ductilityirrespective of the fact that crystallization may, to at least someextent, be present.

In actual practice, it has been definitely determined that by thiscontrol of temperatures, preferably involving an increase in temperatureof the article as it leaves the bath and thereafter a gradual decreasein temperature controllably regulated, the coating is caused to bondfirmly to the article without any danger of crystallization. [By thisprocess, I am enabled to produce articles having a thicker coating, duepartly to the lower bath temperature, and a materially tighter coatingdueto the control of the temperature conditions of the coated article.Also, successive articles have uniform coatings of the desired thicknessand present surfaces not only of uniform color but. of uniformcharacteristics free from spangling and having the desired dull finishcharacteristics.

Further advantages of my invention are inherent in the coating operationin the bath at a lower temperature. As the temperature means, anannealing leer providing controlled increases, with a correspondingincrease in the dross formation and suspension the coating in effect ismore nearly an oxidation of irregular characteristics and without thedesired amount of ductility. By .the coating at a lower temperature, andthereafter subjecting the surfaces of the` coated article to suchtemperature conditions tliatnniformity and ductility is insured, theproduct is correspondingly improved.

Still further advantages of my invention arise from the provision of theheavier coating, it having heretofore been necessary to decrease thecoat thickness in order to produce a dull finish, not only by reason ofthe higher bath temperature but also by reason of the wiping action ofthe rolls used in connection therewith.

Ik claim:

1. In the method of galvanizing, the steps consisting in subject-ing anarticle to the action of a bath of coating material, removing the coatedarticle, subjecting the coated article to sufficient heat in excess ofthe bath temperature to prevent crystallization, and thereaftergradually cooling the coated article by applied heat, substantially asdescribed.

2. In the method of galvanizing, the steps consisting in subjecting anarticle at relatively low temperature to the action of a bath of coatingmaterial, removing the coated article, increasing the temperature of atleast the coating on said article, and thereafter gradually cooling thecoated article, substantially as described. i

3. In the method of producing dull finished galvanized articles, thesteps consisting in coating the articles, removing the coated articlesfrom the-coating zone While conserving the heat thereof and increasingthe temperature, and thereafter gradually cooling the coated articles,substantially as described.

4. In the method of producing dull finished galvanized articles, thesteps consisting in coating an article, removing the article from thecoating zone, increasing the temperature at least of the coating toprevent crystallization thereof, and thereafter controllably cooling thecoated article, substantially as described.

5. In the method of producing dull finished galvanized articles, thesteps consisting in coating an article, removing the article from thecoating zone, increasing the temperature at least of the coating toprevent crystallization thereof, and thereafter cooling theA article bysubjecting the same to gradually decreasing temperature conditions,substantially as described.

6.v A coating apparat-us, comprising coating means, annealing meansproviding controlled temperature gradations, and temperature increasingmeans intermediate said first mentioned means, substantially asdescribed.

7. Coating apparatus, comprising coating temperature gradations,conveying means for transferring a coated article to theleer, and heatincreasing means cooperating with said conveyor, substantially asdescribed.

8. In the method of galvanizing, the steps consisting of passing anarticle through a bath maintained at such temperature that drosssuspension is minimized, thereafter removing said article fiom the bathand increasing the temperature 0f the coating, and effecting gradualcooling of the coated article, substantially as described.

9. In the method of galvanizing, the steps consisting of subjecting anarticle to the action of' a bath of coating material, removing thecoated article, increasing the temperature of at least the coating onsaid article, and thereafter controllin the cooling of the article bypredete'rmine gradations of temperature to produce the desired characterand appearance of the coating. W,

In'testimony whereof I have hereunto Set my hand.

CHARLES A. DAVIS.

